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APPENDIX                                    27I
Grape-sugar.—Although grape-sugar yields neither a bi-
sulphite compound nor gives Scruffs reaction under ordinary
conditions, its properties are for the most part those of an
aldehyde. In addition to its reducing action on copper and
silver salts, and its combination with phenylhydrazine, it forms
an oxime with hydroxylamine and a cyanhydrin with hydro-
cyanic acid. On reduction it gives the hexahydric alcohol
sorbitol, and, on oxidation, the corresponding monobasic acid,
gluconic acid, and the dibasic acid, saccharic acid,
Gluconic acid.                                   Saccharic acid.
The presence of five hydroxyl groups in glucose is determined
by the existence of a pentacetyl derivative. These and other
facts, which cannot be discussed in detail, have led to the adop-
tion of the present formula. The discovery of the optical
antipode of grape-sugar (which is dextro-rotatory) has deter-
mined the present name of dextro-glucose to distinguish it from
laevo-glucose, which is laevo-rotatory. For the synthesis of
these two sugars and the other mono-saccharoses, a text-book
must be consulted.
The other common sugars, which reduce alkaline copper
sulphate, arc fructose (laevulose), galactose, maltose and milk-
sugar, the two latter being disaccharoses. They are most
readily identified by the microscopic appearance and melting-
point of their phenylosazones. Cane-sugar is readily dis-
tinguished from the majority of the common sugars by its
indifference towards alkaline copper sulphate, until previously
boiled with a few drops of dilute sulphuric acid. It is then
inverted and gives the reactions for glucose and fructose.
Bromobenzene. -The replacement of hydrogen by the
halogens Cl and 13r, in the nucleus of aromatic hydrocarbons, is
assisted by the presence of a " halogen carrier," the action of
which has been referred to in the Note on the preparations of
chlor- and brom-acctic acids, p. 252. Iodine, iron, iron and
aluminium chlorides and bromides, the aluminium-mercury